Cage production of broilers has been practiced by the commercial industry since the early 1900's using simple wire cages. Such production met reasonable commercial success as long as live market weights did not exceed 3 pounds. Advances in genetics and nutrition, however, have resulted in live market weights ranging from 3-5 pounds. Birds of this weight, when reared on wire floors or other flat floors, experience a high incidence of foot and leg problems, making them unthrifty. These birds also experience a high incidence of breast blisters caused by resting their keel (breast) bones on flat or sharp surfaces. This adversely affects their market value.
Because of these problems with wire cages, most of the commercial industry in the United States produces broilers using floor pens littered with wood shavings or some other flooring material. This reduces foot and leg problems, as well as breast blisters, to an acceptable level, but creates other problems of concern to the industry. Commercial production of particle board impacts availability and cost of wood shavings as litter. This increases the cost of production, particularly if the litter is not reused. Built-up (reused) litter contains increased disease levels, requiring feed medication to control coccidosis and other diseases. Ultimate disposal of contaminated litter is itself a problem, as are the costs associated with down-time necessary for clean-up and relittering.
Bird production using the litter system is limited to a single level. Multi-level battery brooding cages use wire floors and a separate conveyor belt below to remove manure. Furthermore, at market age the birds must be physically pulled from the cages and carried to waiting bird haul trucks by catch crews, which may result in considerable carcass damage if not done properly. This system, used in Europe, causes considerable mortality in addition to the other problems associated with wire floors, particularly when the birds reach the 3-5 pound weight range. Since this is the current weight range of commercial broilers in the U.S., this system has not been accepted in the U.S. The preferred system in the U.S. continues to be the litter system.